Semiconductor chip stacks can be produced in that two semiconductor chips which each have an upper face that is provided with at least one electronic component and one wiring level are permanently connected to one another with these upper faces facing one another, with connecting contacts on the respective semiconductor chips being directly electrically connected to one another via an interposer or a vertical electrically conductive connection. This arrangement (face-to-face) has the disadvantage that it is difficult to passivate the intermediate space or gap which remains between the semiconductor chips. Such passivation should not impede the rest of the assembly process; in particular, connecting contact pads on a bottom chip should not be contaminated for external connection, for example by means of bonding wires.
The chips are normally passivated using oxinitride and polyimide. However, this requires a subsequent photolithographic opening for the connecting contact pads (bonding pads). Lithography can be carried out only with difficulty on the populated wafers because the wafers which contain the bottom chips that have not yet been separated are difficult to cover with resist layers and to expose once the top chips have been fitted. The passivation process is in particular made more difficult when interconnects on the upper face of the bottom chip lead from the free upper face under the top chips that have been fitted. The connecting contact pads may also be positioned very closely adjacent to the top chips (a few hundred micrometers), so that conventional package encapsulation compounds cannot be used to seal the intermediate space.